1. Field of the Invention
The present invention relates to a digital signal recording apparatus for recording, for example, an audio PCM signal on a magnetic recording medium through a rotating magnetic head.
2. Description of the Related Art
When an audio PCM signal is recorded as a sound signal by a digital signal recording apparatus, if the ratio of the sampling frequency fs to the internal interleave reference signal frequency is not an integer, an image signal and an audio PCM signal are synchronized so that they are properly recorded and reproduced. It is assumed that the audio PCM signal is interleaved in a frame and the sampling frequency fs is 48 kHz. In this case, the frame frequency is 29.97 Hz. Thus, the ratio of these signals is represented as follows. EQU 48000/29.97=1601.6 (1)
Consequently, the ratio of these signals is not an integer.
As an integer that is closest to the quotient, it is assumed that 1602 is designated as the standard number of samples of data recorded at one interleave region. In addition, two numbers of samples numbers, for example 1592 and 1612, are designated as a smaller number and a larger number of the standard number of samples, respectively. The number of samples of the audio PCM signal to be recorded is measured. The cumulative value of the number of samples and the cumulative value of one selected from the designated numbers of sampled are compared in frame frequencies.
When the cumulative value of the number of samples is larger than the cumulative value of the designated value, 1612 is selected. In contrast, when the cumulative value of the number of samples is smaller than the cumulative value of the designated value, 1592 is selected. The selected number of samples are recorded on a recording medium as data for one frame. In addition, an identification signal that represents the number of samples of record data is recorded.
When the sampling frequency fs is 32 kHz, the ratio of the sampling frequency and to the frame frequency is represented as follows. EQU 32000/29.97=1067.7 (2)
Thus, the ratio of these frequencies is not an integer. It is assumed that an integer 1068 that is closest to the quotient is designated as the standard number of samples of data recorded at one interleave region. When two sample numbers 1058 and 1078 are designated as a lower number and a larger number of the standard number of samples, respectively, the above-described sampling frequency fs can be recorded in a similar manner to the case of 48 kHz.
In the above description, it is assumed that two numbers of samples are designated as a lower number and a larger number of the standard number of samples. However, it should be noted that the numbers of sample numbers may be two or more. For example, when the numbers of samples is four, if the sampling frequency fs is 48 kHz, 1622, 1612, 1592, and 1582 may be designated.
When the sampling frequency fs is 32 kHz, four numbers of samples 1088, 1078, 1058, and 1048 may be designated. When more numbers of samples are designated, the above described cumulative values can be more precisely controlled.
Thus, even if the number of samples for one frame is an integer, the number of samples that is close to the above-described standard number of samples is averagely recorded. Thus, asynchronization between the image signal and the audio PCM signal can be prevented. When signals are reproduced, the identification signal extracted from the reproduction signal is cumulated. Thereafter, the phase of the cumulative value is compared with the phase of the cumulative value of the sampling clock formed in PLL (Phase Locked Loop). The compared output is supplied to a VCO (voltage controlled oscillator) of the PLL. Thus, as with the case in the recording mode, the relation between the interleave reference signal and the sampling clock is maintained in the reproducing state, thereby correctly reproducing digital signals.
It is noted that the prior art related to the above-mentioned technique is disclosed in EP laid-open publication No. 561,281 by the same applicant (filing date: Mar. 11, 1993, Application number: 93103963.0 corresponding US Application is pending).
When the sampling frequency fs and the number of quantizing bits Qu are decreased, the number of channels that can be independently recorded can be increased. Now, it is assumed that half the channels are after-recorded. When the sampling frequency fs is 48 kHz, the number of quantizing bits is 16, and the number of channels is 2, the transmission rate of digital data on two channels is represented as follows. EQU 48000.times.16.times.2=1.56 (Mbps) (3)
When the sampling frequency fs is 32 kHz, the number of quantizing bits Qu is 12, and the number of channels is 4, the transmission rate of digital data is represented as follows. EQU 32000.times.12.times.4=1.536 (Mbps) (4)
Thus, these transmission rates in the above-described two cases are the same.
In other words, when the sampling frequency fs is 32 kHz, the number of quantizing bits Qu is 12, the number of channels is 4, and two channels are used during recording, the remaining two channels can be used for after-recording.
However, when after-recording is performed, if the above-described numbers of samples are controlled independently for after recording from that of channels that have been recorded (i.e., not after recording), different identification signals are used. Thus, to such signals, two sets of signal reproducing portions are required.
Therefore, an object of the present invention is to provide a digital signal recording apparatus that can perform after-recording of a digital signal in which the ratio of the sampling frequency fs of a digital information signal to be recorded to the frequency of the internal interleave reference signal is not an integer without requiring a complicated signal reproducing portion.